JP4358701B2 - Induction heating device - Google Patents

Description

  The present invention relates to load temperature detection of induction heating devices such as induction heating cookers and induction heating water heaters.

  Conventional temperature detection device of induction heating device, when detecting the load temperature from the change of the input current, the voltage obtained by subtracting the predetermined voltage of the output of the input current detection means is extracted as the input current change part extraction Means are provided, and the load temperature is detected using the output of the input current change portion extraction means (see, for example, Patent Document 1).

Patent No. 3014181 (4th page, Fig. 3)

In a conventional induction heating device temperature detection device, in order to detect a load temperature from a change in input current, a voltage obtained by subtracting a predetermined voltage from the output of the input current detection means is extracted as a change portion of the input current. Since the partial extraction means is necessary, there is a problem that the input current change partial extraction means having a special circuit configuration must be prepared, leading to an increase in cost.
Further, although the load temperature is detected by using the output of the input current change portion extraction means, it is not intended for the detection of flying, so it cannot be said that the flying detection can be reliably performed. There was also a problem.
The present invention has been made to solve the above-described problems, and it is an object of the present invention to provide an induction heating apparatus that can reliably detect idling without newly providing a load temperature detection means and can avoid an increase in cost. It is what.

An induction heating device according to the present invention includes a rectifier circuit that rectifies an input current from an AC power supply, an inverter circuit that converts an input current connected to an output side of the rectifier circuit into a high-frequency current, and an output side of the inverter circuit A heating coil that is supplied with a high-frequency current to inductively heat the load, an input current detection unit that detects an input current to the rectifier circuit or an input current from the rectifier circuit, and a setting input power signal The detected voltage to the inverter circuit based on the set power generation means, the command voltage converted from the set input power signal generated by the set power generation means, and the detection voltage converted from the input current detected by the input current detection means A drive signal control circuit that outputs a drive signal that matches the command voltage, and a time change amount of the input current detected by the input current detection means It said that the output of the inverter circuit to the drive signal control circuit is constructed by a temperature determination processing circuit for outputting a command for stopping or lowering when exceeding a preset value based on the load impedance caused by Jury temperature It is.

The induction heating device according to the present invention is based on the command voltage converted from the set input power signal generated by the set power generating means by the drive signal control circuit and the detected voltage converted from the input current detected by the input current detecting means. A drive signal is output to the inverter circuit such that the detected voltage matches the command voltage, and the time variation of the input current detected by the input current detection means by the temperature determination processing circuit is based on the load impedance caused by the Curie temperature. When the value exceeds a preset value, a command to stop or lower the output of the inverter circuit is output to the drive signal control circuit, and the output of the inverter circuit is stopped or lowered. The temperature is detected in the form of singularity detection when the temperature is overheated. A.
Further, since the input current detecting means for detecting the load temperature uses the one that detects the existing input current, it is not necessary to provide a new load temperature detecting circuit, and there is an effect that an increase in cost can be avoided.

Embodiment 1 FIG.
FIG. 1 is a block diagram showing the configuration of the induction heating apparatus according to Embodiment 1 of the present invention, FIG. 2 is a flowchart showing the operation of the induction heating apparatus, and FIG. 3 uses a tubular SUS440 as a load of the induction heating apparatus. It is a graph which shows the actual measurement data of load temperature and input current at the time of performing air heating.
In FIG. 1, a rectifier circuit 2 rectifies an input current from an AC power supply 1, and a smoothing capacitor 11 and an inverter circuit 3 are connected to the output side of the rectifier circuit 2.
The inverter circuit 3 includes a pair of switching elements 3a and 3b and a driver 3c that outputs a drive signal to each of the switching elements 3a and 3b. A resonance circuit including a heating coil 4 and a resonance capacitor 12 is connected to the output side of the inverter circuit 3, and a load 5 is disposed near the heating coil 4.

An input current detection means 6 for detecting an input current value from the AC power supply 1 is provided between the AC power supply 1 and the rectifier circuit 2, and a detection signal of the input current detection means 6 is provided in the control means 8. Are input to the temperature determination processing circuit 8a and the drive signal control circuit 8b. The output signal from the temperature determination processing circuit 8a is also input to the drive signal control circuit 8b provided in the control means 8, and the output signal of the drive signal control circuit 8b is input to the driver 3c.
Further, information on the power (thermal power) set by the user of the induction heating apparatus is sent from the set power generation means 7 to the drive signal control circuit 8b.

Next, the operation of the induction heating apparatus according to Embodiment 1 of the present invention will be described with reference to FIGS.
The high frequency current output from the inverter circuit 3 becomes a resonance current by the resonance circuit composed of the heating coil 4 and the resonance capacitor 12, flows through the heating coil 4, and loads the load 5 formed of metal disposed near the heating coil 4. Heat by induction heating.

The heating output at this time is controlled as follows.
First, when the power is turned on, the drive signal control circuit 8b of the control means 8 outputs an activation signal to the driver 3c (step S1). By doing so, the inverter circuit 3 starts to operate, and the input current starts to flow. The input current detection means 6 detects the input current (step S2), and the input current is output to the temperature determination processing circuit 8a and the drive signal control circuit 8b of the control circuit 8.
Next, the set power generation means 7 generates a command voltage IA for the set power information PI by the induction heating device user (step S3) and outputs it to the drive signal control circuit 8b of the control means 8 (step S4).
In the drive signal control circuit 8b, based on the input current detected by the input current detection means 6, it is determined whether or not the DC detection voltage DA converted from the input current matches the command voltage IA of the set power generation means 7. (Step S5).

When the detected voltage DA matches the command voltage IA, the drive signal control circuit 8b continues output to the inverter circuit 3.
Further, when the detected voltage DA does not match the command voltage IA, the inverter circuit 3 so that the detected voltage DA based on the input current by the input current detecting means 6 matches the command voltage IA of the set power generating means 7. By changing the output to, a desired heating output is obtained.

Here, when the load 5 is heated with a desired heating output, the load temperature rises, and the input current slightly decreases as the load temperature rises. This is because the resistivity of the load 5 formed of metal has temperature characteristics, and the load impedance increases as the resistivity increases with increasing temperature.
In the heating operation in the normal state, the change in the input current with respect to the change in the load temperature is small (the input current decreases by about 10% when the temperature rises by 100 deg, see page 2 of Patent Document 1). It is extremely difficult to detect well.

However, when the heating operation is performed in an empty state with respect to the load 5, the load temperature rapidly rises, and when the load material is a magnetic material, the residue remains when the load temperature reaches the Curie temperature (Curie point) determined by the load material. The magnetic flux density becomes zero, and the material properties change greatly because the magnetism is completely lost. An example of the Curie temperature is 850 ° C. for an alnico magnet, 460 ° C. for a Ba-ferrite magnet, 820 ° C. for a samarium / cobalt magnet, and about 360 ° C. for a neodymium magnet.
At this time, the load impedance of the load 5 decreases sharply, and therefore the input current increases sharply.

The graph shown in FIG. 3 is measured data of load temperature and input current when air heating is performed using tubular SUS440 (magnetic martensitic stainless steel) for the load 5.
As shown in FIG. 3, the load temperature rises as the operation of the inverter circuit 3 starts, and the input current decreases as the load impedance increases (up to about 40 seconds elapsed time in FIG. 3). Further, when the load temperature rises, the Curie temperature is reached, and the material characteristics of the load 5 change greatly, so that the load impedance decreases sharply, and therefore the input current increases rapidly (after about 45 seconds in FIG. 3).

As described above, the AC input current detected by the input current detection unit 6 is output to the temperature determination processing circuit 8 a of the control unit 8. In the temperature determination processing circuit 8a, it is determined whether or not the time variation ΔIin of the input current detected by the input current detection means 6 is equal to or greater than the value Y set in advance in the temperature determination processing circuit 8a (step S6).
The time when the time change ΔIin of the input current exceeds the value Y set in advance by the temperature determination processing circuit 8a is regarded as the Curie temperature reaching point, and the temperature determination processing circuit 8a changes the output of the drive signal control circuit 8b. (Step S7), the output of the inverter circuit 3 is stopped or lowered.

In FIG. 3, for example, the time change ΔIin of the input current during the elapsed time 47 seconds to 49 seconds (load temperature about 220 ° C.) is
ΔIin = 12.33-10.54 / 49.0-47.0 = 0.895 [A / sec]
Since the ΔIin value increases rapidly compared to before 47 seconds, the time change ΔIin of the input current detected by the input current detection means 6 also increases rapidly, and this point is reached when the Curie temperature is reached. Considering this as a point, the output of the inverter circuit 3 is stopped or lowered.

  Once the output of the inverter circuit 3 is stopped or lowered, there is a risk that the Curie temperature will be exceeded again even if the output of the inverter circuit 3 is restored. It is desirable not to restore the output of the inverter circuit 3.

  Here, since the output side of the input current detection means 6 is also connected to the drive signal control circuit 8b, the output of the drive signal control circuit 8b according to the output change of the input current detection means 6 based on the load temperature change. However, since the change in the input current with respect to the change in the load temperature is small as described above, the output of the drive signal control circuit 8b is changed by the output (instantaneous value) of the input current detection means 6, and the inverter circuit 3 is stopped. It should be noted that it is difficult to perform power control such as.

  Although the electric circuit in FIG. 1 has a half-bridge configuration of the switching elements 3a and 3b, it is needless to say that the circuit configuration is not limited to this, and the same effect can be obtained even in a full-bridge configuration.

As described above, when the time change of the input current detected by the input current detection means 6 exceeds the value set in advance by the temperature determination processing circuit 8a, the temperature determination processing circuit 8a outputs the output of the drive signal control circuit 8b. Since the output of the inverter circuit 3 is stopped or lowered, the overheated state of the load 5 due to idling or the like can be detected in the form of singularity detection due to the arrival of the Curie temperature, and there is no false detection. Therefore, there is an effect that it is possible to prevent emptying and to secure the safety of the user of the induction heating apparatus.
Further, since the temperature of the load 5 is detected from the time change of the input current value using the existing input current detection means 6 in the induction heating device, it is not necessary to newly provide a special detection circuit, and an increase in cost can be avoided. There is also an effect.

Embodiment 2. FIG.
4 is a block diagram showing a configuration of an induction heating apparatus according to Embodiment 2 of the present invention, and FIG. 2 is a flowchart showing an operation of the induction heating apparatus.
In the first embodiment, the temperature of the load 5 is detected using the time change of the input current value detected by the input current detecting means 6, but this second embodiment is the same as the first embodiment. In addition to 1, the temperature of the switching element of the inverter circuit 3 is detected.

  In FIG. 4, an element temperature detecting element 9a such as a thermistor is attached to the heat radiation fin of the switching element 3a constituting the inverter circuit 3, and the temperature of the switching element 3a is monitored by the element temperature detecting means 9 having the element temperature detecting element 9a. It is what I did. Other configurations are the same as those of the first embodiment, and the description thereof is omitted. In the second embodiment, the element temperature detecting element 9a is attached to the switching element 3a. However, the element temperature detecting element 9a may be attached to the switching element 3b.

Next, the operation of the induction heating apparatus according to Embodiment 2 of the present invention will be described with reference to FIGS.
When the power is turned on, the operation of the element temperature detecting means 9 starts, and the element temperature detecting element 9a detects the temperature of the switching element 3a (step S8). The temperature detection signal of the element temperature detection element 9a is converted into a digital signal by the element temperature detection means 9 and output to the temperature determination processing circuit 8a of the control means 8 (step S4).

An upper limit value of the element temperature is set in advance in the temperature determination processing circuit 8a, and the temperature determination processing circuit 8a determines whether the element temperature detected by the element temperature detecting means 9 is equal to or higher than the preset upper limit value of the element temperature. (Step S8).
When the element temperature detected by the element temperature detecting means 9 reaches the preset upper limit value of the element temperature, the temperature determination processing circuit 8a changes the output of the drive signal control circuit 8b (step S7), and the inverter circuit 3 stops or lowers the output.

Even in the second embodiment, after the output of the inverter circuit 3 is stopped or lowered, even if the output of the inverter circuit is restored, there is a risk that the switching element temperature again exceeds the upper limit value. It is desirable not to restore the output of the inverter circuit 3 unless the power is turned on again.
In addition, about operation | movement of step S1-S6 of FIG. 5, it is the same as that of Embodiment 1, and abbreviate | omits description.

  As described above, according to the second embodiment, the element temperature of the switching element 3a of the inverter circuit 3 is detected by the element temperature detecting means 9, and the detected element temperature is detected by the temperature determination processing circuit 8a. Since the output of the drive signal control circuit 8b is changed when the value is reached and the output of the inverter circuit 3 is stopped or lowered, the element of the switching element 3a of the inverter circuit 3 is added to the effect of the first embodiment. From the viewpoint of preventing overheating of the temperature, the safety of the inverter circuit 3 can be achieved.

Embodiment 3 FIG.
6 is a block diagram showing the configuration of an induction heating apparatus according to Embodiment 3 of the present invention, and FIG. 7 is a flowchart showing the operation of the induction heating apparatus.
In the second embodiment, the switching element 3a (or 3b) of the inverter circuit 3 is controlled so as not to exceed the temperature of the preset upper limit value so as to make the induction heating apparatus safe. In the third embodiment, in addition to the first embodiment, the load 5 is controlled so as not to exceed the temperature of the preset upper limit value, thereby ensuring the safety of the induction heating apparatus.
In the third embodiment, a load temperature detection element 10a such as a thermistor is attached to a load 5 formed of metal as shown in FIG. 6, and the temperature of the load 5 is detected by the load temperature detection means 10 having the load temperature detection element 10a. Are to be monitored. Other configurations are the same as those of the first embodiment, and the description thereof is omitted.

Next, the operation of the induction heating apparatus according to Embodiment 3 of the present invention will be described with reference to FIGS.
When the power is turned on, the operation of the load temperature detecting means 10 starts, and the load temperature detecting element 10a detects the temperature of the load 5 formed of metal (step S10). The temperature detection signal of the load temperature detection element 10a is converted into a digital signal by the load temperature detection means 10 and output to the temperature determination processing circuit 8a of the control means 8 (step S4).

An upper limit value of the load temperature is set in advance in the temperature determination processing circuit 8a, and the temperature determination processing circuit 8a determines whether or not the load temperature detected by the load temperature detecting means 10 is equal to or higher than the preset upper limit value of the load temperature. (Step S11).
When the load temperature detected by the load temperature detection means 10 reaches a preset load temperature, the temperature determination processing circuit 8a changes the output of the drive signal control circuit 8b (step S7) and outputs the inverter circuit 3. Stop or descend.

  Even in the third embodiment, after the output of the inverter circuit 3 is stopped or lowered, there is a risk that the load temperature will again exceed the upper limit even if the inverter circuit output is restored. It is desirable not to restore the output of the inverter circuit 3 unless the power is turned on again. The operations in steps S1 to S6 in FIG. 7 are the same as those in the first embodiment, and a description thereof will be omitted.

  As described above, according to the third embodiment, when the load temperature of the load 5 is detected by the load temperature detection means 10 and the detected load temperature reaches the preset upper limit value in the temperature determination processing circuit 8a. Since the output of the drive signal control circuit 8b is changed and the output of the inverter circuit 3 is stopped or lowered, in addition to the effect of the first embodiment, the load temperature is detected even with the load 5 made of a non-magnetic material. Therefore, since the emptying of the load 5 can be prevented, the safety of the induction heating device user can be further improved.

  In addition to the first embodiment, it is needless to say that the same effect can be obtained even when the element temperature detecting means 9 in the second embodiment and the load temperature detecting means 10 in the third embodiment are used in combination.

Embodiment 4 FIG.
FIG. 8 is a cross-sectional view showing portions of heating coil 4 and load 5 of an induction heating apparatus according to Embodiment 4 of the present invention.
In the fourth embodiment, an induction heating water heater is imitated as an induction heating device.
In the third embodiment, the mounting position and structure of the load temperature detecting means 10 are arbitrary. However, in the fourth embodiment, the mounting position and structure of the load temperature detecting means 10 are limited, and the high frequency that flows through the heating coil 4 is limited. It is intended to prevent erroneous detection due to the alternating magnetic flux generated by the current.
In the fourth embodiment, as shown in FIG. 8, the load temperature detecting means 10 is attached to the inside of the end of the heating coil 4 in the vicinity of the end of the load 5 to monitor the load temperature. In addition, the structure of the induction heating apparatus is the same as that of Embodiment 3, and description is abbreviate | omitted.

Next, the mounting position of the load temperature detecting means 10 will be described with reference to FIG.
An alternating magnetic flux is generated around the heating coil 4 by a high-frequency current flowing through the heating coil 4, and the load 5 is induction-heated by passing through the load 5.
Here, the end portion of the heating coil 4 generates less alternating magnetic flux than the vicinity of the center portion of the heating coil 4 (the magnetic flux density is small). Therefore, when the load temperature detecting means 10 is attached near the end portion of the heating coil 4. It becomes easy to prevent erroneous detection due to induction heating of the load temperature detecting means 10 itself.

However, the degree of heating of the load 5 is greater at the center than at the end of the heating coil 4, and it is difficult to obtain the maximum load temperature when the heating coil 4 is attached to the end. On the other hand, it is desirable to attach the load temperature detecting means 10 to the vicinity of the end of the load 5 by a few mm inside.
In order to prevent erroneous detection due to induction heating of the load temperature detection means 10 itself, the load temperature detection means 10 may be covered with a shield material to have a magnetic-shielding structure.

As described above, according to the fourth embodiment, the load temperature detecting means 10 is attached to the inside of the end of the heating coil 4 in the vicinity of the end of the load 5, so that the induction heating of the load temperature detecting means 10 itself is performed. Thus, the load temperature detection means 10 can detect the load temperature with high detection accuracy.
Further, by covering the load temperature detecting means 10 with a shield material and providing a magnetic-shielding structure, erroneous detection due to induction heating of the load temperature detecting means 10 itself can be further prevented.

  In the fourth embodiment, an induction heating water heater is cited as the induction heating device. However, the induction heating device can also be applied to an induction heating cooker, and the induction heating device in the first to third embodiments is also an induction heating water heater or induction heating. Needless to say, it can be applied to a cooking device.

The block diagram which shows the structure of the induction heating apparatus which concerns on Embodiment 1 of this invention. The flowchart which shows operation | movement of the same induction heating apparatus. The graph which shows the actual measurement data of the load temperature at the time of performing air heating using the tubular SUS440 for the load of the induction heating apparatus. The block diagram which shows the structure of the induction heating apparatus which concerns on Embodiment 2 of this invention. The flowchart which shows operation | movement of the same induction heating apparatus. The block diagram which shows the structure of the induction heating apparatus which concerns on Embodiment 3 of this invention. The flowchart which shows operation | movement of the same induction heating apparatus. Sectional drawing which shows the part of the heating coil 4 and the load 5 of the induction heating apparatus which concerns on Embodiment 4 of this invention.

Explanation of symbols

  1 AC power supply, 2 rectifier circuit, 3 inverter circuit, 3a, 3b switching element, 3c driver, 4 heating coil, 5 load, 6 input current detection means, 7 set power generation means, 8 control means, 8a temperature determination processing circuit, 8b Drive signal control circuit, 11 smoothing capacitor, 12 resonant capacitor.

Claims (5)

A rectifier circuit for rectifying the input current from the AC power supply;
An inverter circuit for converting an input current connected to the output side of the rectifier circuit into a high-frequency current;
A heating coil connected to the output side of the inverter circuit, to which a high frequency current is supplied to inductively heat the load;
Input current detection means for detecting an input current to the rectifier circuit or an input current from the rectifier circuit;
Set power generation means for generating a set input power signal;
Based on the command voltage converted from the set input power signal generated by the set power generation means and the detection voltage converted from the input current detected by the input current detection means, the detected voltage matches the command voltage to the inverter circuit. A drive signal control circuit for outputting such a drive signal;
When the time variation of the input current detected by the input current detection means exceeds a preset value based on the load impedance caused by the Curie temperature, the drive signal control circuit stops or lowers the output of the inverter circuit An induction heating apparatus comprising: a temperature determination processing circuit that outputs a command . A switching element constituting the inverter circuit, and an element temperature detecting means for detecting the temperature of the switching element,
2. The temperature determination processing circuit according to claim 1, wherein when the output of the load temperature detecting means exceeds a preset value, the drive signal control circuit stops or lowers the output of the inverter circuit . Induction heating device. Load temperature detecting means for detecting the temperature of the load that the heating coil induction heats,
2. The temperature determination processing circuit according to claim 1, wherein when the output of the load temperature detecting means exceeds a preset value, the drive signal control circuit stops or lowers the output of the inverter circuit . Induction heating device. 4. The induction heating apparatus according to claim 3, wherein the load temperature detecting means is provided at a location not affected by an alternating magnetic flux generated by a high-frequency current flowing through the heating coil . 4. The induction heating apparatus according to claim 3, wherein the load temperature detecting means has a magnetic shielding structure covered with a shield material .

Images